fix: evict unhealthy provider clients on failed health checks

[dlanov]

/kind bug

What this PR does / why we need it:

Provider gRPC clients are cached after their socket path is discovered. If a provider later moves its socket, the cached client can continue pointing to the old socket and remain unusable until the CSI driver is restarted.

This change:

• snapshots cached provider clients before running health-check RPCs, avoiding holding the cache lock during network calls;
• removes a provider client and connection from the cache when its health check fails;
• closes the failed connection after removing it from the cache;
• verifies the connection being evicted is still the one that failed, preventing an older health-check result from removing a newer connection;
• allows the next Get() call to rescan the configured socket paths and create a new client;
• preserves cached clients when the driver context is being canceled;
• documents that this recovery behavior is available when provider health checks are enabled.

The default value of providerHealthCheck remains false.

Which issue(s) this PR fixes:

Fixes #1821

Testing:

• go test ./pkg/secrets-store -run 'TestPluginClientBuilder_HealthCheck' -count=20
• go test -race ./pkg/secrets-store -run 'TestPluginClientBuilder_HealthCheck' -count=5
• make lint
• make test
• make lint-charts

Special notes for your reviewer:

The new eviction helper compares the cached connection against the connection captured by the failed health check. This avoids deleting a replacement client if another goroutine recreated the provider connection while the health-check RPC was running.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

[kubernetes-prow]

This issue is currently awaiting triage.

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[kubernetes-prow]

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[kubernetes-prow]

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[kubernetes-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: dlanov
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